Apparatus for drawing sheet glass



R. A. MILLER APPARATUS FOR DRAWING SHEET GLASS Filedoct. 11. 1922 2 Sheets-Sheet 1 IN VENTOR I R. A. MILLER APPARATUS FOR DRAWING SHEET GLASS Fneg Oct. 11, 1922 2 sham-she z INVENTOR Patented Jan. 15, 1924.

UNITED STATES PATENT OFFICE.

ROBERT A. MILLER, OF CREIGHTON, PENNSYLVANIA, ASSIGNOR TO PITTSBURGH PLATE GLASS COMPANY, A CORPORATION OF PENNSYLVANIA.

APPARATUS FOR DRAWING SHEET GLASS.

Application filed October 11, 1922. Serial No. 593,721.

To all whom it may concern:

Be it known that I, ROBERT A. MILLER, a citizen of the United States, and a resident of Crei hton, in the county of Allegheny and tate of Pennsylvania, have made a new and useful Invention in Improvements in Apparatus for Drawing Sheet Glass, of which the following is a specification.

The invention relates to improvements in sheet glass drawing apparatus. It is shown as applied to the apparatus of the Hitchcock application Serial No. 493,212, but may be used in any type of sheet forming apparatus in which the sheet is drawn from a bath of molten glass. It has for its principal objects the provisions of a temperature stabilizing or equalizing means for the sheet during its initial formation, and during the period in which its temperature is gradually reduced as the drawing rogresses so that; (1) any sudden variations in temperature at any point of the draw during this period are avoided; (2) the temperature of the sheet from edge to edge and that of the surrounding envelope of gas at any level is maintained substantially constant; (3) warping and cracking are avoided during the period in which the sheet cools down from its temperature of setting through the critical period of annealing or for even a period thereafter; (4) and whereby this stabilizing result is accom lished without interfering with any desire application of heat through the device and without unduly interfering with the visibility of the sheet. One embodiment of the invention is shown in the accompanying drawings wherein:

Figure 1 is the vertical section through the apparatus comprising the improvement; Fig. 2 is a similar section taken at right angles to that of Fig. 1; and Fig. 3 is a side elevation of a small portion of one form of the equalizing curtain employed; and Fig. 4 illustrates another form of ourtain.

Briefly stated the invention involves the use in a sheet drawing apparatus of a metallic curtain which extends from a point adjacent the glass to a point which is as far above the surface of the glass as the requirements of the case call for, such curtain preferably entirely surrounding the sheet, although this is not necessarily the case. This curtain is of a flexible openwork construction, preferably made u r of links, so that the curtain resembles c ain armor, except that it is preferably much more loosely woven and of heavier material. It maybe made of a series of parallel chains secured together by wires, since little or no lateral strength is required in the structure. This curtain surrounding the sheet stabilizes and equalizes the temperature of the gas envelope inside the curtain, so that sudden changes of temperature along the length of the sheet are avoided. The curtain is preferably employed inside of a leer casing to which heat is supplied from a molten bath and also ordinarily from additional heating means, so that the curtain attains a relatively high temperature throughout its length, being hotter, of course, at its lower end and gradually decreasing in temperature upwardly from such point. The curtain thus provides a r ervoir of heat, and drafts or inequalities of temperature which may arise inside the leer casing are prevented from being rapidly transmitted to the glass sheet by reason of the interposed curtain which permits a ready flow of gas or heated air there through, but tempers such air or gas in its passage. The sheet is thus protected from sudden changes of temperature tending to break it or cause it to warp.

It is necessary that the curtain should be entirely flexible, so that it will hang straight, as otherwise the heat conditions would cause the curtain to war bringing it closer at some points to the sheet than at others and thus tending to create inequalities of temperatures upon its interior incident to the varying distances from the glass ribbon or sheet and incident to the fact that any draft upward through the curtain wouldunduly heat the portions of the sheet which are nearest to the curtain. The curtain is of open-work character which also. has the advantage that it has no tendency to produce a draft such as would be roduced by an imperforate curtain, an it further only partially obstructs the view of the sheet, which can be readily observed through the links of the fabric.

Referring to the drawings, 1 is the glass sheet which is to be annealed, such sheet being drawn from the bath 2 contained in slotted member 3, the character of the bath and apparatus'beneath the leer being immaterial in so far as the present invention is concerned. After passing through the leer, which comprises the lower portion 4 and which preferably telescopes inside a second leer section 5, the sheet passes into the drawing device immediately above the leer, the lower portion only of which is shown. This drawing device comprises a pair of endless bands or belts 6 and 7 passing around the pulleys 8 and 9 at their lower ends and about other similar pulleys at their'upper ends. These endless bands consist of suitable chains passing over sprockets and being faced with asbestos member 10 for engaging the surface of the glass. This device serves, not only as a means for drawing the glass through the leer below, but also serves, to a certain extent, as a part of the leer itself. WVhile the glass is designed to pass through its critical temperature in progressing through the sections 4 and 5, it is still at a relatively high temperature when it reachesthe endless belts, and these belts with their asbestos covering serve to maintain the heat of the glass and prevent it from cooling too rapidly.

The lower section 4 of the leer is made up of refractory lining blocks 11 carriedby a suitable framework of commercial sections, including the channels 12 to which the chains 13 are attached, and which serve to support the section at any desired position of vertical adjustment. These chains 13 pass over pulleys 14 and are connected to count'erweights 15. This lower section 4 of the leer may be moved upward inside of the section 5, which is desirable under certain conditions in order to give access to the member 3 and other parts below the leer and in order to act as a regulator for the temperature of the sheet, as the upward movement of the section 4 gives more access of the outer atmosphere to the sheet, so that a chilling effect is secured by adjusting the section upward.

Heating means are employed in the refractory lining 11 opposite the edges of the sheet, such means comprising the passages 16 provided with the gas burners 17. Heating means may also be employed along the sides opposite the sides of the sheet in the form of the nichrome coils 19, shown in Fig. 2. The upper section 5 of the leer is preferably heated electrically by means of the nichrome coils 20. As much additional heat at the lower end of the leer as may be necessary is Supplied by means of the gas burners 21.

The flexible curtain which constitutes the present invention is designated by the reference numeral 22, such curtain'may be made up of a series of vertical ehains23 secured together at their sides by the wires or links 24, as indicated in Fig. 8, or may be of the construction of Fig. 4. The curtain of link construction, as thus provided, is supported at its upper end from the angle iron framework 25 mounted across the upper end of the section 4 and supported thereby, the angle iI'ons constituting the framework having their lower edges perforated to receive the links at the upper ends of the chains constituting the fabric. This fabric extends downwardly as indicated, preferably to'a point within'a few inches of the surface of the molten glass, although this may be varied depen mg upon the amount of chill which it is desired that the sheet should have before it enters the curtain. The curtain, or an additional one, may also be extended upward further, if desired, thus approaching the bolts 6 and 7 and by adjusting the length and number of curtains (one inside the other) the device may be made to act as a leer. The distance which the curtain is spaced from the sheet will depend upon varying conditions, but this will ordinarily be 2;]; or 3 inches. The weight of the links constituting the fabric will also vary, depending upon conditions, and this fabric may be made lighter or heavier as desired and its open-work character'increased or decreased as conditions may require. In some cases it may be sufii cient to make the curtain in two'sections without any connecting portions extending around the edges of the sheet, but ordinarily the curtain will be made in continuous form completely encircling the sheet.

To initiate the drawing operation a bait is lowered between the endless belts 6 and 7 and down through the curtain 22 and into the molten bath, the glass adherin to the bait which is then drawn up unti it passes between the endless belts, after which the drawing is continued by reason of the grip of the belts u on the opposite sides of the sheet. The g ass ribbon or sheet," as it passes out from between the two endless belts at their upper ends is cut intosections of convenient size for handling.

The use of the flexible curtain tends to eliminate any warping orbreaking .of' the sheet intermediate the glass bath and the endless belts 6 and 7. After the sheet enters the belts 6 and 7 at a relatively greatly reduced temperature as comparedwith the temperature at the lower end of the section 4, there is little tendency to warp or break as the sheet is practically annealed, having passed through the critical period of annealing. The flexible curtain, because of its heat retaining capacity and becauseof the shielding function which itwperforms, serves to prevent any highly localized changes of temperature in the sheet such as would otherwise tend to cause it to warp and break. Any drafts or relatively cool air tending to strike the sheet must first pass through the heated fabric and in such passage the temperature of the flowing gases are materially modified. so that the sheet is protected in a large degree from accidental rapid local cooling. Similarly, the sheet is protected from any undue local heating in the leer incident to changes in gas pressure or other causes and which would also tend to adversely aflect the sheet. Other advantages incident to the construction will be readily apparent to those skilled in the art.

What I claim is:

1. In apparatus for drawing sheet glass from a bath of molten glass, means for drawing a sheet upwardly from the bath, and temperature stabilizing means for the sheet comprising a flexible open work metal curtain surrounding the sheet and extending upwardly from the bath.

2. In apparatus for drawing sheet glass from a bath of molten glass, means for drawing a sheet upwardly from the bath, and temperature stabilizing means for the sheet comprising a flexible open work metal curtain of link construction entirely surrounding the sheet and extending upwardly from the bath.

3. In apparatus for drawing sheet glass from a bath of molten glass, means for drawing a sheet upwardly from the bath, temperature equalizing means in the form of a flexible open work curtain surrounding the sheet and extending upwardly from the bath, and heating means for the sheet out side the curtain.

a. In apparatus for drawing sheet glass from a bath of molten glass, means for drawing a sheet upwardly from the bath, temperature equalizing means in the form of a flexible open work curtain surrounding the sheet and extending upwardly from the bath, a leer casing surrounding the curtain, and means for applying heat to the interior of the casing.

In testimony whereof, I have hereunto subscribed my name this 22nd day of September, 1922.

ROBERT A. MILLER. 

